The present invention relates generally to surge protection systems and methods. More particularly, the present invention relates to providing multiple levels of surge protection for a power supply by sensing changes in an input voltage over time and sensing a DC voltage of the power supply.
Electronic power supplies are vulnerable to high voltage surges caused, for example, by lightning strikes. One defense to high voltage surges caused by lightning strikes is to provide outdoor surge protection. One standard for outdoor surge protection is the ability to withstand a 6 kV or 10 kV surge from a combination wave generator.
Two-stage half-bridge type converters or inverters are used widely in power supply design. FIG. 1 illustrates an exemplary embodiment of a related art power supply with a half-bridge type inverter/converter having a surge protector. When a high voltage surge appears across the line and neutral of the input Vac, even with a surge protector a high voltage is presented across capacitor C1 and the voltage rail. A surge protector is connected in parallel with the input Vac to limit the voltage to the rest of the circuit. Without any further protection, semiconductor components, particularly switches Q1 and Q2, may be damaged by the surge because switches Q1 and Q2 are designed to meet a steady state voltage requirement. For example, if the rail voltage V_rail is around 470 volts DC, a 600 volt-rated switch Q1 and a 600 volt-rated Q2 will be used. If the rail voltage V_rail exceeds 600 volts during a surge condition, switches Q1 and Q2 will be easily damaged and cause failure of the entire circuit or system.
Diodes D1-D4 together form an input rectification circuit that converts the AC input voltage to a DC rail voltage. Capacitor C1 is a high frequency filter capacitor. A power factor correction (PFC) stage 120 is coupled between the input and second stage half-bridge DC-DC converter.
Switches Q1 and Q2 form a half-bridge DC-DC converter in FIG. 1. Switches Q1 and Q2 may take the form of any type of switching device, such as a MOSFET, a BJT, an IGBT, etc. The integrated circuit (IC) 130 is a half-bridge drive IC. The voltage Vcc represents the power supply input of the IC 130. IC 130 typically has a disable pin to turn off the gate drive signal. A load 140 (or power tank) is connected to the output of half-bridge (e.g., between the switches Q1 and Q2). The PFC stage 120 regulates the input current to achieve a high power factor, as well as to provide a stable DC rail voltage (V_rail) to the half-bridge DC-DC converter.
What is needed in the art is a fast triggering surge protection circuit in a power supply whose AC input is already connected to an existing surge protection means to provide protection for switching components.